This invention relates generally to corrosion inhibitors, and in particular to corrosion inhibitors and processes of using the same to protect metal surfaces in oil and gas drilling systems.
Servicing fluids, also known as completion or packer fluids, are used in many oil and natural gas wells for a variety of purposes. Completion fluids used in oil and gas well drilling and similar applications in oilfields include drilling muds, brines, water, oil, and the like. Completion fluids can include inorganic salts, such as halides of zinc, calcium, sodium and other alkali elements, in concentrations ranging from trace amounts up to saturation.
Corrosion is recognized as a problem in the development of geoenergy sources, including oil and natural gas reserves, geothermal and geopressured systems. The corrosion problems are aggravated by the presence of acid gases such as hydrogen sulfide and carbon dioxide and by the co-production of brine solutions. For example, carbon steel is widely used in the construction of oil and gas wells in oilfields. While a useful material for such applications, carbon steel corrodes due to the presence of electrolytes and water in many servicing or completion fluids. In recent years, corrosion problems have become more severe as production from deeper, high pressure and high temperature wells has become more attractive, as these deeper formations can have increased levels of acid gas fluids.
Additives can provide corrosion protection for metals used in oil and gas drilling systems, such as carbon steel. However, conventional additives do not always provide the desired degree of corrosion protection, particularly at higher temperatures.
For example, corrosion inhibitors used in oil and gas drilling operations have typically included organic compounds containing nitrogen, sulfur and/or phosphorous. These corrosion inhibitors protect metal surfaces at least in part by forming a protective film on the metal surface. Thus, an important consideration for corrosion protection in oil and gas drilling systems is how well the corrosion inhibitor is transported to the corroding surface within the oil or gas well system. Dispersibility of the inhibitor in completion fluids, such as brine solutions, also plays an important role in its corrosion protection performance. Many other factors, such as stability of the protective film and inhibitor concentration in the completion fluid, are also important to provide enhanced corrosion protection. Many current inhibitors, however, have limited stability, particularly at higher temperatures, or exhibit poor characteristics in the solution and therefor offer limited protection.
The present invention provides corrosion protection for metal surfaces present in oil and gas well drilling systems. One embodiment of the invention includes brine solutions useful in oil and gas well drilling systems and similar applications, for example, as completion fluids. In one aspect of this embodiment of the invention, the solutions include at least one heteropoly complex anion of transition metal elements as a corrosion inhibitor.
The invention also includes solutions that include a mixture of at least one heteropoly complex anion of transition metal elements with at least one additional corrosion inhibiting additive or agent. For example, the solution can include a mixture of at least one heteropoly complex anion of a transition metal element and at least one other transition metal compound as corrosion inhibitors. As another example, the solution can include a mixture of at least one heteropoly complex anion of a transition metal element and at least one compound of the metallic elements of the groups IIIa to VIa of the Periodic Table of Elements as corrosion inhibitors. Preferred compounds of the metallic elements of Group IIIa to VIa include halides of Group Va, and more preferably antimony halides, such as antimony bromide.
In another aspect of this embodiment of the invention, the solutions can include at least one compound of a metallic element of Group IIIa to VIa, and preferably of Group Va, of the Periodic Table of Elements. Exemplary compounds include without limitation oxides, sulfides, halides, nitrates, and the like, preferably halides, of metallic elements of Group IIIa to VIa. Preferably the solutions include halides, and more preferably antimony bromide (SbBr3), as a corrosion inhibition additive.
The brine solutions of the invention containing the above noted corrosion inhibitors can provide improved corrosion protection for metal surfaces found in oil and gas drilling systems. The noted corrosion inhibiting additives can be stable in the solution phase, providing desired additive concentrations, stability and improved dispersibility. Still further, use of the solutions in oil and gas wells and other similar applications can result in a protective layer containing magnetite (iron oxide) formed on carbon steel. The inventors have found that a protective layer which forms as a result of using the solutions of the invention can be more corrosion resistant than the oxide layer formed in the presence of conventional corrosion inhibitors, such as lithium molybdate, in which magnetite film tends to be more amorphous and less developed. In addition the solutions of the invention can minimize or eliminate pitting of metal contacted with the brines. The solutions are particularly useful at high temperatures, approaching 550xc2x0 F. and higher.
The present invention also provides processes for inhibiting corrosion metal surfaces present in oil and gas drilling systems and similar applications using the above noted corrosion inhibitors.